Is this PSU okay for my 300W graphics card?

These people don't know what they're talking about the watts aren't spread out for all the hardware devices, it's just the level that each hardware device will run at. If you're graphics card requires 300W the PSU will downgrade itself to run at 300W, it's kinda like the speed limit on the roads 60MPH is the max to drive but you can still drive slower without running into problems with the law. It's just not recommended to use a lower PSU for instance a 200W, that way your devices won't be running at full potential.